Crystallization and spectroscopic characterizations of binary SrO-B2O3 glasses doped with LiF, NaF, CaF2, or TiO2

Abstract

Glasses based on the basic chemical composition of binary strontium borate (SrO 50-B2O350 mol%) together with samples containing dopant (2%) with one of the fluorides (LiF, NaF, CaF2) or TiO2 have been synthesized through the routinely melting and annealing technique. Collective structural, optical, and thermal properties have been measured for the prepared glasses. X-ray diffraction and SEM measurements were carried out for their corresponding glass-ceramics which were synthesized by controlled thermal heat treatment with two-step regime. FT infrared absorption spectra reveal composite vibrational modes in the mid-range 400–1600 cm−1 which are related to the co-presence of both triangular and tetrahedral borate building units in their particular different wavenumber sites. The low dopant level did not make any distinct variations in the IR spectra. X-ray diffraction patterns elucidate the formed crystal phases after crystallization mainly strontium metaborate and other related borate phase and the LiF shows no distinct variation while NaF2 and CaF2 induce the formation of additional crystalline Na-containing or Ca-containing phases besides the formation of NaF or fluorite (CaF2). TiO2 acts as a nucleating agent and also separate as rutile. The crystallization behavior has been correlated with the assumption of the tendency of SrO to induce phase separation in the host binary borate glass and controlled heat treatment initiates the separation of strontium metaborate crystalline phase in the base binary SrO-B2O3 in accordance with its composition and the role of dopants is found to be varying with the type of dopant. The measured thermal expansion parameters of the prepared glasses reveal variations in their values for transformation and softening temperatures depending on the type of added dopant. The changes in the thermal expansion coefficients in the different parts of the thermal curves are related to the ability of the network to absorb lattice expansion through bending of the bonds. The uniform observed ultraviolet absorption bands are related to traces of iron (Fe3+) ions present as impurities.